Medical diagnostic and intervention systems in neurology, angiography and cardiology nowadays use many X-ray devices or pieces of X-ray equipment as a basis for imaging. X-ray devices are frequently equipped with what is referred to as a C-arm. A C-arm usually comprises an X-ray source, also known as an X-ray emitter, and an X-ray detector positioned opposite by a connecting support embodied in the shape of a letter C. The C-arm can be mounted to a stand or to the ceiling and can be moved to different positions by jointed connections. In X-rays an object being examined, e.g. a patient, is irradiated with X-ray beams. If X-ray beams penetrate a body, they are attenuated or absorbed to varying degrees depending on the material involved, such as bones, different types of tissue or fluid, so that when the X-ray detector is struck, different intensity patterns or images are produced corresponding to the materials penetrated.
When material is penetrated, radiation supplies energy to the surrounding atoms or molecules. Electrons from the atomic shells can also be struck and chemical bonds can be broken. Radicals are produced, which for their part can again cause damage. Difficult examinations or interventions, such as for example clamping an aneurysm in a neurosurgical operation, often require frequent irradiation of the affected body region over an extended period of time. This means that the patient is subjected to significant radiation exposure or radiation levels. Added to this is the difficulty that a physician performing the treatment is reluctant to alter the position of the X-ray device which is favorable in terms of imaging, which means that the same region of the body is constantly irradiated over a long period of time. This can lead to radiation damage in the volume of the body region being irradiated and to a heating of the irradiated area or surface which may even amount to skin burns. This is also referred to as a hotspot, which is created by the X-ray fan beam.
In practice, after a certain number of X-ray recordings, a physician will alter the recording direction, which is also described as the projection setting of the X-ray device, e.g. by rotation of the C-arm, in order to distribute the radiation levels over a larger volume or a larger surface area. This, however, presupposes a considerable amount of experience and discipline on the part of the physician.
Modern X-ray devices offer the possibility, under the abbreviation CARE, which stands for Combined Applications to Reduce Exposures, to add together the radiation doses of several X-ray recordings and to issue a warning if a limit is exceeded. The disadvantage of these systems is that even if the changes to the projection setting are only slight, e.g. when turning the C-arm by one or two degrees, the sum of the radiation applied is reset to zero, even though a point may continue to be radiated when the position of the C-arm has been slightly altered.